A Rho-dependent phase-variable transcription terminator controls expression of the FimE recombinase in Escherichia coli
A Rho-dependent phase-variable transcription terminator controls expression of the FimE recombinase in Escherichia coli
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DOI：
10.1046/j.1365-2958.2002.03081.x
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发表时间：
2002-08-01
影响因子：
3.6
通讯作者：
Dorman, CJ
中科院分区：
文献类型：
--
作者：
Joyce, SA;Dorman, CJ
fim开关是一个314 bp的可逆染色体DNA片段，负责大肠杆菌1型菌毛的相位可变表达。开关含有fimA基因的启动子。这编码1型菌毛亚基蛋白，并且当启动子指向fimA（开启阶段）时，细菌是有菌毛的，并且当其被引导离开时，细胞是无菌毛的。开关位于fimE基因的下游，编码酪氨酸位点特异性重组酶，催化开关从ON到OFF阶段的反转。先前已经提出，因为fim开关位于fimE基因的下游，所以FimE的表达可以在关闭期细菌中受到反义RNA的控制，其中fim开关内携带的启动子与fimE基因的转录方向相反。在本研究中，未检测到诱导型fimE反义RNA（顺式或反式表达）对FimE表达的影响。在相ON细胞中，fimE mRNA延伸穿过开关进入fimA，而在相OFF细胞中，它终止于开关内。这种终止是Rho依赖性的，并且在Rho突变体中被废除。在ON期细胞中发现的延伸的fimE更稳定，并且与OFF期细菌相比，导致FimE蛋白质增加约5倍。在不存在Rho因子的情况下，fimE mRNA在ON期和OFF期细胞中同样稳定，并且FimE重组酶的水平也相等。
The fim switch is a 314 bp segment of invertible chromosomal DNA that is responsible for phase-variable expression of type 1 fimbriae in Escherichia coli. The switch harbours the promoter of the fimA gene. This codes for the type 1 fimbrial subunit protein and, when the promoter is directed towards fimA (phase ON), the bacteria are fimbriate and, when it is directed away, the cells are afimbriate. The switch lies immediately downstream from the fimE gene, coding for a tyrosine site-specific recombinase that catalyses inversion of the switch from the ON to the OFF phase. It has been suggested previously that, because the fim switch lies immediately downstream from the fimE gene, expression of FimE could be subject to control by antisense RNA in phase OFF bacteria in which the promoter harboured within the fim switch is oriented against the direction of transcription of the fimE gene. In this study, no effect of inducible fimE antisense RNA, expressed in cis or in trans, on FimE expression was detected. In phase ON cells, fimE mRNA extends across the switch into fimA, whereas in phase OFF cells, it terminates within the switch. This termination is Rho dependent and is abolished in a rho mutant. The extended fimE found in phase ON cells is more stable and results in an approximately fivefold increase in FimE protein compared with phase OFF bacteria. In the absence of Rho factor, fimE mRNA is equally stable in phase ON and phase OFF cells, and the levels of FimE recombinase are also equal.